A non profit organization that represents tech startups and the general tech community has spoken out against rights-holder calls in the U.S. for piracy filters to be made mandatory for internet service providers and websites.

The non-profit, Engine, says that not only are piracy filters prone to false positives, they will also be so costly that it will hurt nascent companies and stifle innovation in the process.

"Reversing two decades of sensible copyright policy to require OSPs to deploy tools that are costly, easily circumvented, and limited in scope would deeply harm startups, users, and content creators alike," says Engine.

In Engine's report, the startup lobby group cites a recent case study which found a false positive rate of 1 to 2 percent when piracy filters are used.

This may not sound like a lot, but considering many sites deals with millions of user generated files, this could lead to tens of thousands legitimate files being filtered for no reason.

"Accordingly, a 1–2 percent false positive rate for an automated filtering procedure is problematic for the same reasons, as such a technique would result in filtering legitimate content at rates that would frequently obstruct speech," Engine's report states.

Engine also estimates the cost of implementing a filter for a medium sized file sharing service would be $10,000 and $25,000 in licensing fees alone, something that will be out of reach for smaller startups.

So an mandatory filter could end up being an expensive foible that's prone to false positives could also be easily made redundant, with new file formats escaping the filter's attention, and it would also not stop sites outside of the U.S. not beholden to the country's copyright laws from offering pirated files.